NEW YORK, July 7 (Reuters) - He is a former altar boy, now in his 30s, who says a small-town parish priest won his trust, sexually abused him, often violently, and left him too ashamed to tell anyone for years.

It is the kind of allegation that has shaken the Roman Catholic Church and other institutions and led to trials, convictions and millions of dollars in civil settlements.

The difference, in this case, is that the former priest, Gary Mercure, cannot be charged or tried in court because his alleged crimes occurred in New York, where state law gives victims of child sex abuse only until they are 23 years old to make a complaint.

It is one of the most restrictive statutes of limitation nationwide.

Now, with the convictions of former Penn State assistant football coach Jerry Sandusky and Philadelphia Monsignor William Lynn putting a powerful spotlight on pedophilia, activists and victims hope they can finally change that law and pursue cases that have been out of reach.

"It's a slap in the face to see somebody walk away from it," said a California restaurant worker, who alleges a decade of abuse by Mercure, starting when he was an altar boy aged 7 or 8.

"The Sandusky thing brings everything back up," he added. It is Reuters' policy not to identify victims or alleged victims of sex-related crimes.

Mercure was convicted last year of raping two altar boys in Massachusetts, where he took them across state lines from New York, and was sentenced to more than 20 years in prison. His lawyer could not be reached for comment.

A handful of others have also accused the former priest of abuse . T he restaurant worker says he can name as many as 20 victims, all altar boys, in his hometown on the shores of Lake George.

New York Democratic Assemblywoman Margaret Markey said the successful prosecution in the Sandusky and Lynn cases should bolster her so-far frustrated efforts to extend the statute's age limit to 28 for civil and criminal cases. Sh e also seeks to give alleged victims shut out by the existing law a one-year window to pursue civil claims.

"I think what has happened in Pennsylvania is going to have a major impact," she said, adding that many victims of child sex abuse "can't find justice in this state."

In New York, many felony cases must be brought within five years. In 1996, the law was changed so the five-year clock did not begin running until child sex-abuse victims turned 18.

Several states have no time limits on such cases. Victims can take years struggling with shame, self-recrimination, guilt and other emotions before they come forward, experts say.

New Jersey law requires child sex abuse lawsuits be filed within two years of the victim turning 18, but exception is made if the victim can prove the memories only surfaced as an adult and realizes emotional damage was caused.

In New York, Markey's bill has passed the Assembly four times, but the Senate version has never come up for a vote.

LOOK-BACK WINDOWS

Her measure has run into stiff opposition, largely over the inclusion of the one-year window allowing anyone who alleges abuse - no matter how long ago - to pursue a civil case.

Such a window, for instance, could have paved the way for legal action against Brooklyn Poly Prep over claims that a football coach at the private school molested dozens of boys over a period of 25 years. It could mean New York's Horace Mann School and its staff would face lawsuits related to recent allegations that teachers there abused students years ago.

In California, a one-year window led to hundreds of cases filed against churches, youth groups and other organizations.

New York's Roman Catholic Church is among the loudest critics of the proposed New York reform.

"The Church does oppose look-back windows, that would allow a case to be brought alleging abuse, from literally, 30, 50, 75 or more years ago," Joseph Zwilling, spokesman for the Archdiocese of New York, said in an email.

"Statutes of limitations exist for a reason. It is nearly impossible to defend against a claim from so long ago, when the accused is dead, the accused superiors are all dead, memories faded, evidence gone," he wrote.

Instead, the Church supports another bill extending the age limit to 28, with no window, said New York State Catholic Conference spokesman Dennis Poust. That proposal has been working its way through the state legislature for several years.

Another of Mercure's accusers, a finance worker in his late 30s who says he too was abused for a decade, believes the ability to bring lawsuits dating from crimes committed years ago would help victims gain some closure.

"You're trying to do everything you can do to be productive at work, productive at home ... yet have this big dark black cloud following you wherever you go," he said.

MORE COMING FORWARD

Jeanine Pirro said that most of of the child sex abuse cases she saw in her 12 years as district attorney in Westchester County, just north of New York City, "were well past the statute of limitations."

"The child would take a while to reveal, and the parents would take a while to believe and then confront, then the Church would delay it in many cases," said Pirro, who now hosts "Justice with Judge Jeanine" on Fox News.

A growing number of victims - some who suffered years ago - may step forward to reveal abuse in the aftermath of the Sandusky and Lynn cases, experts said.

"With every successful criminal conviction, every successful civil award, I think you get more awareness of the extent of this problem," said Tina Weber, a Philadelphia-area attorney who represents child sex abuse victims.

Sandusky, who faces the possibility of more than 400 years in prison, was convicted last month of molesting 10 boys over a period of 15 years. Had his case been in New York, three of his victims most likely would have been excluded due to the statute.

Pennsylvania law allows civil charges to be filed until victims are 30 years old and criminal charges to be filed until victims turn 50 in child sex abuse cases.

Lynn, who authorities say covered for sexually predatory priests, was convicted on the same day as Sandusky of child endangerment. His case involved two grand juries, the first of which found abuses that could not be prosecuted due to limitations in place at the time.

For the Catholic Church, the stakes are high. In the Archdiocese of New York, the nation's second largest, about 60 priests have been accused of predatory behavior toward children, according to the Bishop Accountability Project, which documents cases of abuse in the Roman Catholic Church.

'A VERY PAINFUL LESSON'

A more realistic number should be more than 10 times higher in the archdiocese, where some 7,500 priests have worked since 1950, said the group, which calculates that in dioceses with more open disclosure, the percentage of accused priests tends to be nearly 10 percent.

Still, some former prosecutors give the church high marks when it comes to pursuing sex offenders.

Lisa Friel, former chief of the Manhattan District Attorney's sex crimes unit, said the Church was very cooperative in cases that could not move legally. It helped with locating accused predators, determining if they had access to children and warning potential employers, she said.

"We had a very good working relationship with the Archdiocese in New York," said Friel, now a consultant on sexual misconduct in the private sector for T&M Protection Resources.

The archdiocese spokesman said it had "excellent working relations" with area district attorneys. The Church encourages anyone with a claim of abuse to go to authorities and, if it knows of such abuse, will contact authorities as well, he said.

"The Catholic Church has learned a very painful lesson, and we want to help others who are looking to combat this evil," he wrote. "We were once, perhaps, a good example of how NOT to handle abuse; please God, we can now be an even better example of how to prevent the abuse of children."

A change in New York's law might bring some relief, said Mercure's California accuser, but he added: "It doesn't change anything as far as how you live your life and the nightmares and the therapy."

"All that stuff, that doesn't go away." (Additional reporting by Daniel Wiessner in Albany and Joseph Ax in New York; Editing by Paul Thomasch and Peter Cooney)